1. Field of the Invention
This invention relates to a method of preparing ceramic microspheres, more particularly to a method of enabling preparation of true spheres with uniform particle size of submicron order without using ceramic fine powders as a starting material and adjustment of the desired mean particle size by suitably selecting a frequency of ultrasonic waves.
2. Description of the Related Art
As this kind of method, U.S. Pat. No. 4,746,468 discloses a method in which ceramic microspheres can be prepared by dispersing an aqueous suspension of ceramic fine powders as droplets in a high boiling point liquid which has substantially the same specific gravity as the suspension and which is immiscible with water and nonreactive with the ceramic fine powder. Furthermore, Japanese Unexamined Published Patent Application No. 62-262734 teaches a method in which ceramic microspheres are obtained by dispersing an alcoholic suspension or sol of ceramic fine powders as droplets in a liquid paraffin and thereafter evaporating the alcohol.
These methods are surely advantageous in that ceramic microspheres of true spheres with uniform particle size can be obtained but disadvantageous in that mean particle size of the obtained ceramic microspheres depends on the orifice bore because of dispersing the suspension of ceramic fine powders as droplets in the high boiling point liquid through the orifice. Consequently, these methods can only produce ceramic microspheres with comparative large particle size ranging from several .mu.m to over 10 .mu.m.
Moreover, the above-mentioned two methods are defective in that the particle size of ceramic fine powders for forming the suspension must be always much smaller than that of the aimed ceramic microspheres and consequently ceramic fine powders produced by a special method for example an alkoxide-hydrolysis method must be used.